1. Field of the Invention
The present invention relates to a battery charging method and particularly to a technology for effectively shortening the charge time and suppressing deterioration in the life of the battery.
This application is based on patent application No. Hei 11-321803 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, hybrid vehicles that are provided with a motor in addition to an engine as a power source for running the vehicle, and electric vehicles that are provided solely with a motor as a power source for running the vehicle are known.
Because these vehicles drive a motor using electric power supplied from a battery, it is necessary to charge the battery when the remaining battery charge (state of charge) is reduced due to electric discharge.
When charging a discharged battery, in order to safeguard the battery, it is recommended that the charging be carried out for approximately 10 hours at one tenth of the rated capacity (0.1C). Because rapid charging of the battery leads to deterioration of the battery and a reduction in the lifetime thereof, it has not been very common.
In particular, it has been common with electric vehicles to charge the battery using nighttime power for use on the following day.
However, rapid charging of the battery is demanded in cases such as if the vehicle needs to be suddenly used during the night, or in order to recharge the battery after driving in order to continue to drive the vehicle (i.e. in order to extend the distance driven).
In cases such as these, if the charge current is increased excessively, because the allowable temperature during charging (i.e. the upper temperature limit without harming the battery) ends up being reached due to the heat given off by the battery, the charge current cannot be excessively increased. This is because if the allowable temperature is exceeded, the charging efficiency is reduced and it is not possible for the battery to be charged substantially. Alternatively, due to overcharge reaction, the battery temperature suddenly increases which has a deleterious effect on the battery life.
To counter this, battery cooling apparatuses (a cooling fan or the like) for cooling the battery during charging have been considered, however, because the cooling performance is insufficient, it has not been possible to sufficiently radiate the heat generated by the battery charging leading naturally to a limit on the charge current.
Moreover, as is shown in FIG. 8, if the allowable temperature limit during charging is reached, then a process of temporarily stopping the charging, waiting for the temperature to go down, and then starting the charging again has been repeated over and over and, in some cases, this has led to the charge time instead becoming lengthened.
If the charge time is lengthened, in this way, the problem arises that a waiting time is generated in the use of the apparatus and the usability thereof suffers.